1. The problem statement, all variables and given/known data In this diagram, the net force on the 1.0 mC charge is zero. What is the sign and magnitude of the unknown charge q? Please see attached photo. 2. Relevant equations F = KQ1Q2/r^2 3. The attempt at a solution I have approached this by first determining the force required by “q” on the middle particle to maintain the system in its current position. Because the 2 bottom particles cancel in the “x” direction the combined force they place on the middle particle is 2Fy? And so “q” must also place a force of 2Fy but in the -y direction on the middle particle. So by this rationale I should be able to calculate the charge of “q” using q = (2Fy)(r^2)/(k)(Q1) where Q1 is the middle particle. q = (8.65 x 10^6 N)(0.0009 m^2) / (9.0 x 10^9 N M2/C2)(1.0 x 10^-3 C) = 8.65 x 10^-4 C positive charge? I am assuming I do not have to use the vector method to determine the force of q because it also has equal components in both the - and + x directions which cancel. So net force is just in the y direction and this is used to calculate the charge? The magnitude of this charge seems low to me, I would have expected a more symmetrical charge. Should I be considering the forces between q and the bottom two particles?